Syrian Civil War spillover in Lebanon

The Syrian Civil War spillover in Lebanon occurred from 17 June 2011 to 28 August 2017 when the Syrian Civil War spilled over into Lebanon as pro-Assad (mostly Shi'ite, leftist, and Palestinian groups) and pro-Syrian Opposition factions (mostly Sunni Islamist groups) battled across Lebanon in a resurgence of sectarian violence. The ensuing conflict lasted six years, and it ended in August 2017 when the last al-Qaeda affiliates and Islamic State fighters were expelled from Lebanon by the Lebanese Army.

Background
Following the Lebanese Civil War and the 2005 Cedar Revolution, Lebanese politics was divided between the pro-Syria March 8 Alliance and the anti-Syria March 14 Alliance. Tensions ran high following the assassination of the anti-Syria Prime Minister Rafic Hariri in 2005, resulting in the 2008 Lebanon conflict. The 2008 Doha Agreement led to both factions of Lebanese politics agreeing to appoint consensus candidate Michel Suleiman as President, and the Shi'ite parliamentary opposition was granted a veto power and more parliamentary representation.

However, the breakout of the Syrian Civil War in 2011 led to the reignition of sectarian tensions in Lebanon as millions of Syrian refugees fled into the country. The civil war saw most of Syria's Sunni population rise up against the Alawite-dominated Ba'athist government of President Bashar al-Assad, who was a strong ally of Lebanon's powerful Hezbollah political party and militant group. The March 14 Alliance, led by the predominantly-Sunni Future Movement and the Maronite Lebanese Forces party, called for Lebanese aid to the Free Syrian Army and to take a stronger stance against the Syrian government. The ruling March 8 Alliance, dominated by Hezbollah and the Maronite Free Patriotic Movement, rejected this move, leading to protests breaking out across Lebanon and Sunni protesters burning Hezbollah flags and images of Hezbollah Secretary-General Hassan Nasrallah.

Conflict
As the civil war escalated in 2011, black market arms sales skyrocketed, and clashes between Sunnis and Alawites in Tripoli in June 2011 left 7 people dead. As the Syrian Islamist opposition gained strength in 2013, Sunni extremists from Tripoli flocked to Syria to join the al-Qaeda affiliate, the al-Nusra Front, leading to Hezbollah fighters being deployed to border towns to protect the local Shia villagers from Sunni militants. The Lebanese Army attempted to remain neutral during the conflict, lest it break up along sectarian lines as it had done during the civil war of the 1970s and 1980s. In Tripoli, the rivalry between the Sunni Bab al-Tabbaneh and Alawite Jabal Mohsen districts led to a series of suicide bombings and armed clashes between the communities, and, while Jabal Mohsen became adorned with posters of Assad, Arab Democratic Party leader Rifaat Eid, and Syrian flags, Bab al-Tabbaneh soon flaunted jihadist flags, martyrdom posters for Islamist suicide bombers, and posters of Sunni leaders such as the Iraqi dictator Saddam Hussein and the Future Movement leader Saad Hariri.

In June 2014, a joint brigade of al-Nusra Front and Islamic State militants invaded and briefly held the town of Arsal, and, on 2 August 2014, al-Nusra militants raided Lebanese Army checkpoints and captured parts of northeastern Arsal, leading to a Lebanese Army counterattack with Syrian air support. The Lebanese Army recaptured Arsal after five days of fighting with the two Islamist groups, who were rivals in Syria but "frenemies" in Lebanon. In June 2015, al-Nusra and IS once again seized territory in Lebanon, leading to battles between the Sunni Islamist militant groups and Hezbollah; the Islamist groups also fought each other. By 22 June 2016, 95% of the territory lost to the Sunni Islamist groups had been reclaimed by the government, and daily clashes occurred near the town of Arshal, which was still an Islamist stronghold. On 22 September 2016, IS leader Imad Yassin was captured in the Ain al-Hilweh refugee camp, and, on 26 October, clashes broke out between IS and al-Nusra in the Arsal Barrens after IS attempted to infiltrate the Hamid Valley. On 28 October, the Lebanese Army destroyed an IS hideout in the Wadi Zarzour area of Jaroud Arsal, and, on 24 November, IS commander Ahmed Youssef Ammoun was captured at his temporary headquarters near Arsal. On 21 July 2017, the Syrian Arab Army and Hezbollah launched a joint campaign to recapture Islamist territories along the Syria-Lebanon border near Qalamoun, while the Lebanese Army assumed a defensive position in Arsal. On 22 July 2017, Hezbollah captured the Tahrir al-Sham (al-Nusra's successor) base at Dhahr al-Huwa. On 27 July, a ceasefire deal was agreed upon, under which the Tahrir al-Sham forces would withdraw from Lebanon to Idlib Governorate in Syria, Saraya Ahl al-Sham would withdraw to the eastern Qalamoun Mountains, and prisoners would be exchanged by both sides. On 27 August 2017, the remaining IS holdouts in the western Qalamoun agreed to a ceasefire with the Lebanese Army and Hezbollah, and, the next day, the IS fighters burned their headquarters in the area and were transferred for al-Bukamal in the eastern Syrian desert. For the first time in six years, the Lebanese government was once again in control of all of Lebanon.